Ontological arguments are arguments, for the conclusion that God exists, from premises which are supposed to derive from some source other than observation of the world—e.g., from reason alone. In other words, ontological arguments are arguments from what are typically alleged to be none but analytic, a priori and necessary premises to the conclusion that God exists.
St. Anselm, the Archbishop of Canterbury, made a fair share in the long list of proofs for proving the existence of God. He made an argument wherein it completely relies on one’s understanding of God to prove its actual existence; this is popularly known as the Ontological Argument
St. Anselm, in his Proslogion, unknowingly formulated what appear to be two arguments. It was not clear to him that the first argument he laid down was completely different from the 2 second argument, for he had seen it merely as an elaboration of the first one. “However, most philosophers today think that he stumbled on a completely different, and perhaps, stronger line of reasoning”.
The two arguments begin with the same initial premises but takes a different direction as it goes further. The first argument “purports to prove, simply from the concept of God as the supreme being, that God’s existence cannot rationally be doubted by anyone having such a concept of Him.”
The second argument “makes the stronger claim that God exists necessarily, or in other words, God possesses a kind of existence that is possessed by no other thing.
The first argument goes like this: I have an idea of God. This idea of God is the idea of a being that is the greatest that can be conceived. A being is greater if it exists in reality than if it exists only in the understanding alone. If God, who is the greatest conceivable being, exists in 3 the understanding alone, then a greater being that exists in reality can be conceived. But this is a contradiction. It is absurd to conceive of a being which is greater than the greatest conceivable being.
According to second argument-God, the greatest possible being, is the one whose existence does not depend on anything else. This implies that God “cannot begin to exist and cease to exist” (Lawhead 2007, 9) and also, God does not just happen to exist but exists necessarily. Therefore, God exists and “thou canst not be conceived not to exist; and rightly. For if a mind could conceive of a being better than thee, the creature would rise above the Creator; and this is most absurd.
In brief the argument can be explained as –
Anselm’s Ontological Argument
(1) God is that than which no greater can be conceived.
(2) If God is that than which no greater can be conceived then there is nothing greater than God that can be imagined.
Therefore:
(3) There is nothing greater than God that can be imagined.
(4) If God does not exist then there is something greater than God that can be imagined.
Therefore:
(5) God exists.
The first premise of this argument, (1), is Anselm’s conception of God. (2) is a simple logical truth; if God is the greatest conceivable being then there is no greater conceivable being. (3) follows simply from (1) and (2).
Anselm argues in support of (4) by comparing a non-existent God with an existent God. An existent God, says Anselm, is greater than a non-existent God. If God were non-existent, therefore, then we could imagine a God greater than he, namely an existent God.
(5) follows simply from (3) and (4).